1. Field of the Invention
The present invention relates to a semiconductor light emitting diode, such as a light emitting diode (LED) or a laser diode (LD). More specifically, the present invention relates to a semiconductor light emitting device having its light output surface made rough.
2. Description of the Related Art
Conventionally, a high intensity LED has been fabricated by forming a double-heterostructure light emitting region on a semiconductor substrate and then forming a current diffusing layer on the light emitting region. For this reason, packaging the high intensity LED with a resin results in a structure in which the top of the current diffusing layer is covered with the passivating transparent resin.
With such a structure, the critical angle associated with the current diffusing layer (the refractive index is in the range of 3.1 to 3.5) and the vitreous resin (the refractive index is of the order of 1.5) is in the range of 25 to 29 degrees. Of light that travels from the light emitting region toward the vitreous resin, the light that strikes the layer—resin interface at angles larger than the critical angle will suffer total internal reflections. This will significantly reduce the probability of light produced within the LED being emitted to the outside. At present, the probability (light output efficiency) is of the order of 20%.
There is a method of improving the light output efficiency by forming a film of high refractive index on the current diffusing layer to thereby increase the critical angle. However, even with this method, an increase in the efficiency is low, of the order of 20%.
Thus, the conventional LEDs that are packaged with transparent resin material suffer from the problem that the light output efficiency is low. This is because, at the interface between the transparent resin and the top layer of semiconductor multi-layer structure including a light emitting layer, most of the light that strikes the interface at angles suffers total internal reflections. This problem is common to surface-emitting LDs.